New 80 volt push mowers

[StinkyGoalieGuy]

In case anyone is interested, thanks to Metallover's post and link to the logic analyzer from Amazon, I was able to decode the battery signal from the "Omega" port on a Greenworks 60V battery. I recreated the signal using an Arduino and hooked up the Greenworks Brushless leaf blower using a 18S1P A123 LiFe battery and it worked!

Here is the Arduino code:

// written 5/26/2020
// Working battery interface signal from the "Omega" port
// of a Greenworks Pro 60V battery

#define PIN 6

void setup()
{
pinMode(PIN, OUTPUT);
}

void loop()
{

digitalWrite(PIN, HIGH);
//Delay 188,000us
for(uint8_t i = 0; i < 188; i++)
{
delayMicroseconds(1000);
}

digitalWrite(PIN, LOW);
delayMicroseconds(400);

for(uint8_t i = 0; i < 3; i++)
{
digitalWrite(PIN, HIGH);
delayMicroseconds(100);
digitalWrite(PIN, LOW);
delayMicroseconds(200);
}

for(uint8_t i = 0; i < 9; i++)
{
digitalWrite(PIN, HIGH);
delayMicroseconds(100);
digitalWrite(PIN, LOW);
delayMicroseconds(100);
}

delayMicroseconds(100);

for(uint8_t i = 0; i < 1; i++)
{
digitalWrite(PIN, HIGH);
delayMicroseconds(100);
digitalWrite(PIN, LOW);
delayMicroseconds(200);
}

// 5
for(uint8_t i = 0; i < 4; i++)
{
digitalWrite(PIN, HIGH);
delayMicroseconds(100);
digitalWrite(PIN, LOW);
delayMicroseconds(100);
}
delayMicroseconds(100);

for(uint8_t i = 0; i < 4; i++)
{
digitalWrite(PIN, HIGH);
delayMicroseconds(100);
digitalWrite(PIN, LOW);
delayMicroseconds(200);
}

for(uint8_t i = 0; i < 3; i++)
{
digitalWrite(PIN, HIGH);
delayMicroseconds(100);
digitalWrite(PIN, LOW);
delayMicroseconds(100);
}

digitalWrite(PIN, HIGH);
delayMicroseconds(1000);
digitalWrite(PIN, LOW);
delayMicroseconds(200);

for(uint8_t i = 0; i < 2; i++)
{
digitalWrite(PIN, HIGH);
delayMicroseconds(100);
digitalWrite(PIN, LOW);
delayMicroseconds(100);
}
delayMicroseconds(100);

for(uint8_t i = 0; i < 1; i++)
{
digitalWrite(PIN, HIGH);
delayMicroseconds(100);
digitalWrite(PIN, LOW);
delayMicroseconds(200);
}

for(uint8_t i = 0; i < 2; i++)
{
digitalWrite(PIN, HIGH);
delayMicroseconds(100);
digitalWrite(PIN, LOW);
delayMicroseconds(100);
}

delayMicroseconds(100);

for(uint8_t i = 0; i < 4; i++)
{
digitalWrite(PIN, HIGH);
delayMicroseconds(100);
digitalWrite(PIN, LOW);
delayMicroseconds(100);
}

delayMicroseconds(100);

for(uint8_t i = 0; i < 3; i++)
{
digitalWrite(PIN, HIGH);
delayMicroseconds(100);
digitalWrite(PIN, LOW);
delayMicroseconds(100);
}

delayMicroseconds(100);

for(uint8_t i = 0; i < 2; i++)
{
digitalWrite(PIN, HIGH);
delayMicroseconds(100);
digitalWrite(PIN, LOW);
delayMicroseconds(100);
}

delayMicroseconds(200);

for(uint8_t i = 0; i < 1; i++)
{
digitalWrite(PIN, HIGH);
delayMicroseconds(100);
digitalWrite(PIN, LOW);
delayMicroseconds(100);
}

delayMicroseconds(100);


}

 

[fastcrille]

Hi

I have tried this "code 5/26/2020" on arduino mega to simulate BMS signal for my 80v greenworks mower, it works.
I run it with my ebike 18s LIPO with out any problem...

Thanks for the solution!
(Metallovers code doesent work, there is some thing wrong with it)

 

[StinkyGoalieGuy]

Cool! Thanks for the feedback. Good to see somebody using it.

 

[pizzy00]

The latest code will keep my Kobalt 80v chainsaw from erroring out(red led with yellow exclamation mark) by start button, but if I keep it on full throttle for a say around 30 seconds it shuts off. I bought the same analyzer and have captured some data. However I'm not that great at coding though. Can anyone help? I really want to use my own lipos for this.

I also have a harbor freight atlas 80v chainsaw but it doesn't stay on, so must have different pwm bms signal. I could captures some signals on this of anyone was interested.

What speed should I sample rate and what trigger? Any tips appreciated.

 

[pizzy00]

I have some nice samples now. So I will try to refine and tweak the code to see if I can keep the chainsaw working.

 

[pizzy00]

Yeah still no luck. I guess I'll jist bypass esc totally and use a vesc I have. Will be nice, I'll have a wireless controller for my chainsaw lol. I should be able to run it fine.

 

[StinkyGoalieGuy]

If you put the logic analyzer on the output of the arduino, does the wave match what you saw coming out of the battery?

 

[Jay33]

First of all, thank you guys for this amazing resource! This is like jackpot for anyone trying to play with this mower!

Q, I only got the motor and PCB Board. didn't get the switch box, I thought, i would control it from Ardunio anyway. but now i realize I need the on/off protocol (for white/black/blue wire). Before I blind try myself... anybody has any idea how to on/off/throttle without the switch box? Also are there any more states other than on and off?

Thanks again

 

[veloman]

First of all, thank you guys for this amazing resource! This is like jackpot for anyone trying to play with this mower!

Q, I only got the motor and PCB Board. didn't get the switch box, I thought, i would control it from Ardunio anyway. but now i realize I need the on/off protocol (for white/black/blue wire). Before I blind try myself... anybody has any idea how to on/off/throttle without the switch box? Also are there any more states other than on and off?

Thanks again

I believe the switch box is a simple on/off switch. I'm not sure which wires get shorted.

 

[StinkyGoalieGuy]

Do you mean you bought the switch box from Greenworks?

I'm just repeating the same pattern over and over that I pulled off with the logic analyzer. So no special turn on sequence.

First of all, thank you guys for this amazing resource! This is like jackpot for anyone trying to play with this mower!

Q, I only got the motor and PCB Board. didn't get the switch box, I thought, i would control it from Ardunio anyway. but now i realize I need the on/off protocol (for white/black/blue wire). Before I blind try myself... anybody has any idea how to on/off/throttle without the switch box? Also are there any more states other than on and off?

Thanks again

 

[Jay33]

I believe the switch box is a simple on/off switch. I'm not sure which wires get shorted.

Thanks for reply. yes thats what i need to figure out. if I can get some confirmation from you guys that would be much better than trying to randomly short it.
Also sometimes the squeeze bar connect to potentiometer to give more power to as you pull the lever harder. this one could be just on off as you said. As i have no clue.

so as you know there are three wires to the switch box connector. white, black and blue.
with battery connected and no short, white (+) to black (-) or white(+) to blue (-) both reads 32 volts
blue to black reads 0 volts
and no continuity between either of these wires.

any idea whats my best bet when i start shorting them! ?

Do you mean you bought the switch box from Greenworks?

No. I do not have a switch box.
I already had a greenworks 80v battery. I bought motor and the PCB control box from greenworks.
Now im trying to figure out how to start it without switch box.
Please correct me if i understood wrong, but as understand the signal pattern is for non-greenwoks battery without the ohm input. As I already have an original greenworks battery. I think i don't need that.


here is the 1000 words

 

[Jay33]

I think i figured it out.
Basically all three wires need to be connected.
first connect black and blue wires together, then connect/disconnect the white wire to on/off
Order seems to matter for subsequent on/off.
Means if you disconnect black/or blue instead of white, then once its off it will not turn on again (by connecting black/blue back) until battery reconnected.


if you like to on/off with an ardunio+relay, simply connect black and blue together to one connector of the relay and white to the other connector.

 

[veloman]

Has anyone got these batteries figured out? Mine was working fine I I think I reversed the connection to my mower and blew the fuse. I was able to replace the fuse and it shows 78v now but it won't charge. Charger light doesn't come on at all but the battery meter lights up as usual. Same result on two chargers.
My blower will run for 3 seconds then shut off. This almost sounds like the communication is not happening. Maybe I damaged one of the boards...

 

[BradKdr]

Hi All,

First off, thanks everyone for the work you have done and for sharing it here.
I just bought a Greenworks 60V Self Propelled mower and am trying to convert it to run on 3 Ryobi 18V batts in series.
When I connect the batts it shows 4 bars (fully charged) on the handle of the mower.
When I turn it on it runs for about 3 seconds then shuts off and beeps 3 times.
I even connected it to a variable power supply set to 60V and get the same thing.

I found this forum, bought an Arduino Nano, uploaded the program and hooked it up to the 3rd terminal on the mower.

I know the Arduino is providing a signal but the mower is still doing the same thing (Shutdown after 3 seconds then beep beep beep.........beep beep beep.).

Any help would be greatly appreciated here...Anyone know what the 3 beeps mean?

I think I've narrowed the problem down to the signal or the motor controller...I bought the mower used and think it was a store return but I don't know for sure.

 

[spinningmagnets]

How old is the battery? maybe it cant pull the amps it used to when it was newer...

 

[BradKdr]

Batteries are new and can handle up to 30A.

I'm sure its not the batteries as I have the same problem when I press the switch without turning on the motor.
After 3 seconds I get a beep beep beep.......beep beep beep....

I am starting to wonder if my motor controller as bad since others here have been able to get theirs working with the Arduino, I have the same problem no matter what I do.

 

[jgoedhard]

Those controllers look caked with goo. I wonder if just replacing the controller with something of a more programable friendly board would solve a bunch of issues. And $14. 3 Phase motor. 80 volts.

I was going to perform a shunt to try and get an increase in speed but after seeing those pictures of the controller. I don't think I want to try the attempt and would rather replace the controller and add a variable speed selector.

Would be something if replacing the shunt with a variable resistor would do anything to keep that blade spinning fast.

 

[plmicia]

I have bought Powerworks 60V mower cheap without battery.
My idea was to run it with 3x Makita 18V batteries which I have a lot.

To make it run I have modified Arduino sketch available on Endless sphere thread.
I simply removed second part of a script to check if the answer form mower will still appear on a bus. Indded it was.



Unfortunatley this was not enough for reliable opration. Mover turns off after 1-2 min of running with 6 loud beeps.

Reading carefull this thread and eevblog theread I figure out that query frame is not the same all the time.
Dumb luck I was able to generate different random query and sitll receive answer from mower.

https://youtu.be/Y7Tlfim-A8w

I tried to alternate this query every 2sec. and to my surprise it works!
I was able to mow grass in my entire garden for ~60min.

https://youtu.be/ER4f0lgI0SA

Preliminarly I was worried about lack of power in battery powered mower.
Mower draws only ~5A continous, 10A max and this reflecs to only 300 - 600W of power, compared to 2-3kW gas powered mowers.
However it turns to be opposite - gas powered mowers seems to be overpowered for such simple task as grass cutting .

BTW. to power Arduino form 5V you do not need separete DC/DC 60V to 5V converter.
5V is available at motor hall sensor harness!



Here is my working Arduino sketch:

// written 5/26/2020
// Working battery interface signal from the "Omega" port
// of a Greenworks Pro 60V batter


//20.05.2021 BornToRepair/plmicia mod:
//reply frame removed
//pin6 input mode enabled beetween query frames
//query cycling each 2000ms

#define PIN 6

void setup()
{
pinMode(PIN, OUTPUT);
}

void loop()
{

for(uint8_t a = 0; a < 10; a++)

{
digitalWrite(PIN, HIGH);
//Delay 188,000us
for(uint8_t i = 0; i < 188; i++)
{
delayMicroseconds(1000);
}


pinMode(PIN, OUTPUT);

digitalWrite(PIN, LOW);
delayMicroseconds(400);

for(uint8_t i = 0; i < 4; i++)
{
digitalWrite(PIN, HIGH);
delayMicroseconds(100);
digitalWrite(PIN, LOW);
delayMicroseconds(200);
}

for(uint8_t i = 0; i < 10; i++)
{
digitalWrite(PIN, HIGH);
delayMicroseconds(100);
digitalWrite(PIN, LOW);
delayMicroseconds(100);
}

delayMicroseconds(100);

for(uint8_t i = 0; i < 1; i++)
{
digitalWrite(PIN, HIGH);
delayMicroseconds(100);
digitalWrite(PIN, LOW);
delayMicroseconds(100);
}

// 5
for(uint8_t i = 0; i < 3; i++)
{
digitalWrite(PIN, HIGH);
delayMicroseconds(100);
digitalWrite(PIN, LOW);
delayMicroseconds(100);
}
delayMicroseconds(100);

for(uint8_t i = 0; i < 2; i++)
{
digitalWrite(PIN, HIGH);
delayMicroseconds(100);
digitalWrite(PIN, LOW);
delayMicroseconds(200);
}

for(uint8_t i = 0; i < 1; i++)
{
digitalWrite(PIN, HIGH);
delayMicroseconds(100);
digitalWrite(PIN, LOW);
delayMicroseconds(100);
}

for(uint8_t i = 0; i < 1; i++)
{
digitalWrite(PIN, HIGH);
delayMicroseconds(100);
digitalWrite(PIN, LOW);
delayMicroseconds(200);
}

for(uint8_t i = 0; i < 3; i++)
{
digitalWrite(PIN, HIGH);
delayMicroseconds(100);
digitalWrite(PIN, LOW);
delayMicroseconds(100);
}

pinMode(PIN, INPUT);
}



for(uint8_t a = 0; a < 10; a++)
{
digitalWrite(PIN, HIGH);
//Delay 188,000us
for(uint8_t i = 0; i < 188; i++)
{
delayMicroseconds(1000);
}
pinMode(PIN, OUTPUT);

digitalWrite(PIN, LOW);
delayMicroseconds(400);

for(uint8_t i = 0; i < 3; i++)
{
digitalWrite(PIN, HIGH);
delayMicroseconds(100);
digitalWrite(PIN, LOW);
delayMicroseconds(200);
}

for(uint8_t i = 0; i < 9; i++)
{
digitalWrite(PIN, HIGH);
delayMicroseconds(100);
digitalWrite(PIN, LOW);
delayMicroseconds(100);
}

delayMicroseconds(100);

for(uint8_t i = 0; i < 1; i++)
{
digitalWrite(PIN, HIGH);
delayMicroseconds(100);
digitalWrite(PIN, LOW);
delayMicroseconds(200);
}

// 5
for(uint8_t i = 0; i < 4; i++)
{
digitalWrite(PIN, HIGH);
delayMicroseconds(100);
digitalWrite(PIN, LOW);
delayMicroseconds(100);
}
delayMicroseconds(100);

for(uint8_t i = 0; i < 4; i++)
{
digitalWrite(PIN, HIGH);
delayMicroseconds(100);
digitalWrite(PIN, LOW);
delayMicroseconds(200);
}

for(uint8_t i = 0; i < 3; i++)
{
digitalWrite(PIN, HIGH);
delayMicroseconds(100);
digitalWrite(PIN, LOW);
delayMicroseconds(100);
}
pinMode(PIN, INPUT);
}
}

 

[Xetra]

Hi all
I bought a 40v trimmer and would like to power it with a 40v ninebot es2 extra battery. Work only for 3 sec ....
Is anyone able to scan the omega signal from 40v battery ?
I bought the greenworks bms and I will feed 40v from the ninebot battery (and maybe use a single 18650 cell to "fake" other ghost cells)
https://fr.aliexpress.com/item/1005003021191625.html?spm=a2g0o.productlist.0.0.6e82be37Ov2npT&algo_pvid=eea47441-b1fb-4691-aee5-bbb4fe91b056&algo_exp_id=eea47441-b1fb-4691-aee5-bbb4fe91b056-10

 

[5net]

My mower just stopped working (no warranty, bought used). Right now, it ran and then started beeping repeatedly. So I used another battery to test if it was a defectives battery. Turned out, it was the bad PCB controller board.
I went shopping around and can't find the board anywhere



I wonder if anyone every try to use a controller box from e-bike to make it work around?
https://www.ebay.com/itm/142551852200

Or maybe build a simple circuit to just run it?

Have anyone ever try that?

Thanks.

 

[amberwolf]

I wonder if anyone every try to use a controller box from e-bike to make it work around?
https://www.ebay.com/itm/142551852200

Assuming it is a BLDC 3-phase type of brushless motor, you could probably use any EV/ebike type brushless controller that can supply the amps needed from startup, that will run from the voltage range the Kobalt packs provide.

If the motor is loaded (mower sitting on grass), it could take quite a lot of power to get the blade moving up to speed, and similarly if it hits a heavy patch it'll also take a lot. How much depends on the system; some can take hundreds of amps for just a second or less, some only take dozens for that time period...but a typical cheap ebike controller may shutdown (or fail!) from overcurrent before it finishes starting up. Depends on the controller design.

It may only take a few amps to keep it running once started, and when only cutting normal grass..but the startup under load might be pretty high.

Since your controller doesn't work we can't test what it had to provide under real-world conditions. If we can find out what specific motor is in there, or the ratings for the original controller, it will help us find you one that will work.

Or maybe build a simple circuit to just run it?

That depends on what's wrong with the original controller, and whether you can build a circuit to bypass or emulate that.

There isnt' really a simple circuit to run a brushless motor, though; it's much much simpler to get an existing controller than to build one from scratch.

If it had been brushed, then even just a switch would do it, as long as it could handle the amps and volts without welding shut.


But before you get into all that...the most common problem with anything electrical is connections and wiring. It is possible that one of the plugs or wires from the controller to the motor, etc., has an intermittent or open connection, and this is causing the controller to not detect something it requires, and error out.

I would first try unplugging and replugging each of the connectors on the controller in turn, before repowering it with a battery. The most likely one to cause a problem is the one with the gray ribbon cable; the crimps on the pins of it's connector (either the controller side or the other one) could be poor or wire could break there or pull out, etc).

If the motor has hall sensors (and that's probably the cable for them if so), it could also be a sensor in the motor that has failed, either actually failed or just has a poor connection.

But it could also be a phase FET in the controller that has failed; it may be a bridge module under the large heatsink rather than separate FETs; in either case it may be repairable if you're up for that (but it might not be).

 

[5net]

Assuming it is a BLDC 3-phase type of brushless motor, you could probably use any EV/ebike type brushless controller that can supply the amps needed from startup, that will run from the voltage range the Kobalt packs provide.

Thank you for your response.

On my guess, I believe this is a Brushless DC motor: 3 wires coming on the right Red/Black/Yellow.
(The left Black/Yellow from the battery case/ far left Red is from batterty to Fuse Key)
Red: hot
Black: ground
Yellow: NTC?



I found this on the box that I think the motor is rated at 72V nominal voltage.



I measured the voltage on the battery it shown ~78V



Here is what I found on the PCB board:



My plan I was use a cheap "72V 1000W E-bike Brushless DC Motor Speed Controller" ~$33 to work around, without using any ebike parts.






Do you think this is possible?

 

[5net]

I also found a youtube videos of a teardown and a test with 48V battery/controller

 

[amberwolf]

On my guess, I believe this is a Brushless DC motor: 3 wires coming on the right Red/Black/Yellow.
(The left Black/Yellow from the battery case/ far left Red is from batterty to Fuse Key)
Red: hot
Black: ground
Yellow: NTC?

If it's a brushless 3-phase motor, then it doesn't have a hot and a ground, it has three AC power wires, called phases.

All three are driven equally with pulses of the right timing and current to make it spin.

There is often another cable with 5 or more wires for hall sensors that are used to detect motor position to help with the timing. These are called sensored motors. Ones without these are sensorless; that's what yours would be, if it is a BLDC with magnets in the rotor, since it has no other wires from it to the controller.

If the motor is not a BLDC, with magnets in the rotor, but instead is a type of induction motor (no magnets), then a cheap ebike controller won't run it. It would need a specific controller that will run the specific motor type.

It is also possible that it isn't a 3-phase motor at all, and is some other type, and it uses the third wire for something else (like you suggested, a temperature sensor). That's not likely, but possible.

I found this on the box that I think the motor is rated at 72V nominal voltage.

That's helpful, as it means you should be able to buy a "72v" brushless controller to run it, once we know how much current it needs.

If it's helpful to you, the chart is really showing what the batteries do as they go from full to empty.

Here is what I found on the PCB board:

270966528_1263191084512974_4340993522935694398_n.jpg

My plan I was use a cheap "72V 1000W E-bike Brushless DC Motor Speed Controller" ~$33 to work around, without using any ebike parts.
s-l1600.jpg
Capture.PNG
Do you think this is possible?

As noted before, it depends on how much startup power it has, and what motor type it actually is.

That particular controller has a hall sensor connector, which means it probably works only wiht motors that also have one.

Assuming your motor actually is a BLDC (with magnets) 3phase brushless motor, then you would need a sensorless controller, because your motor doesn't have them.

I would guess that 1000w might work ok, but we don't know for sure how much current the motor will take. Might not need that much power, might need more. A 72v 1000w controller only outputs 13A.

Do you know what the max amps (or watts) the batteries are able to output? (most have some sort of limit; it may or may not be listed on them anywhere). Also, how many batteries does this motor take at once to run? (some take 2, from what I saw on google, but couldn't tell if those were the same as yours).


There are some wiring things from the old controller that won't do what they did before, or wont' be connected at all, and there is one thing you will need to add that isn't there. Some of them you'll need to do some tests with a multimeter to find out how they're wired on the mower, to be able to hook up the controller to them.

Presumably the hand control you ahve now does not change the motor's speed, and only goes either full on, or off. If that's the case, you can use a potentiometer between the hand control and the controller's throttle input to fake an ebike controller into going full speed without getting any errors from not having an actual throttle. We'll worry about that after figuring out which controller will work for your system.

If the "safety switch" is literally just a switch that closes when engaging the mower's safety lever/etc, you can connect the "ebrake" wires to that so it disables the controller when not using it. If it's more complicated, we'll need to figure out what exactly it does before hooking it up to anything.


If that 3-wire connector for safety switch / bail lever is actually going to two switches, then the one for safety can be ebrake, and the bail lever (if that' syour hand control to operate the motor) can operate the throttle input of the controller. If it's only one switch, then you'll need to use it to operate the throttle.


THe storage switch, if it's just a switch that opens when it's on, can be used to connect the "keyswitch / ignition / switch plug" wire on the controller to the battery positive, which enables the controller when the switch is closed (shorted).

THe battery capacity indicator wont' have anywhere to plug into the new controller, so it isn't going to do anything. If the batteries have their own indicator on them, you can use that to check level while mowing, periodically.

If you need a battery indicator, then there is another way to "hack one on", and take care of the throttle/potentiometer problem at the same time. You can buy an ebike thumb or half-grip throttle that has a battery meter built into it, that is designed for 72v. (it can't be for other voltages or it won't measure correctly, unless it is an actual voltmeter--if it's a bar or dot level meter, it's must be preset for the right voltage). Then you mount this on the mower where you can see the meter on it. YOu don't have to operate the throttle, just set it to maximum, and glue or screw it into position. (then it gets wired between the hand control and the throttle input of controller).

 

[5net]

If it's a brushless 3-phase motor, then it doesn't have a hot and a ground, it has three AC power wires, called phases.
...

Assuming your motor actually is a BLDC (with magnets) 3phase brushless motor, then you would need a sensorless controller, because your motor doesn't have them.

Thank you very much for you response again. I have learned a lot for the last 2 days.
In some other Kobalt models, they use "a 3ph Permanent Magnet motor with hall effect rotor position sensors."
This one definitely doesn't those position sensors. Only 3 wires, I will assume they are 3phase brushless dc sensorless.
but I am really trying to figure it out what type of motor is this, so I disassembled the housing to look for a label and took couple of photos.
It is impossible to find any information on it. Do you think you can identify what type of this motor base on this photo?

Do you know what the max amps (or watts) the batteries are able to output? (most have some sort of limit; it may or may not be listed on them anywhere). Also, how many batteries does this motor take at once to run? (some take 2, from what I saw on google, but couldn't tell if those were the same as yours).

Only 1 battery at the time. The battery is a Kobalt 80V 5.0Ah 360W (at 72v * 5 = 360W?)

There are some wiring things from the old controller that won't do what they did before, or wont' be connected at all, and there is one thing you will need to add that isn't there. Some of them you'll need to do some tests with a multimeter to find out how they're wired on the mower, to be able to hook up the controller to them.
---
If you need a battery indicator, then there is another way to "hack one on", and take care of the throttle/potentiometer problem at the same time. You can buy an ebike thumb or half-grip throttle that has a battery meter built into it, that is designed for 72v. (it can't be for other voltages or it won't measure correctly, unless it is an actual voltmeter--if it's a bar or dot level meter, it's must be preset for the right voltage). Then you mount this on the mower where you can see the meter on it. YOu don't have to operate the throttle, just set it to maximum, and glue or screw it into position. (then it gets wired between the hand control and the throttle input of controller).

These are super helpful, some of them was what I am trying to achieve.
For now, I am trying to figure it out if ebike controller will work with this, so I can order the controller.
Kobalt Greenworks 80v Lawn Mower Motor 48v Testing
https://www.youtube.com/watch?v=3OUSs3yd2XY
I found this video, and look like it is a 48v ebike controller making the motor running with come series batteries.
One is from a Greenworks 80v motor with hall sensors like the one in this thread page 3, but he doesnt hook them to anything

Another one is from Kobalt 80V without sensors.
I think this is very promising for what I am doing.



I also found some brushless motor lokk similar to this mower motor that can be control with the ebike controller.